金相分析结果表明：45钢电机转轴肩部出现的脱裂属淬火裂纹，是由于淬火介质的温度较高，浓度低，冷却能力明显下降，使转轴淬火时，在肩部和根部（及端面中部）存在组织差异，冷却时在转轴肩部产生局部的附加拉应力所造成。此外，原材料存在疏松缺陷，横向强度下降，亦促进脱裂的形成。最后提出了相应对策。 Metallographic analysis results show that: 45 steel motor shaft shoulder cracking occurs quenching cracks, quenching medium is due to the high temperature, low concentration, cooling capacity decreased significantly, so that the shaft quenching, the shoulder and root (and the end face Central) there are organizational differences, resulting in the cooling shoulder in the local additional stress generated. In addition, raw materials are loose defects, lateral strength decreased, also contributed to the formation of cracking. Finally, the corresponding countermeasures are put forward.